1. Field of the Invention
The present invention relates generally to multistaged prevaporizing pre-mixing fuel injectors, and more particularly, to a fuel injector especially suitable for combustion of high flame speed fuels.
2. Description of the Prior Art
Fossil fuels have been widely used in power generation and other combustion applications. Alternatives to fossil fuels for production of power include use of renewable fuels. For example, one class of fuels is the syngas produced through gasification of feedstocks which results in fuel streams rich in hydrogen. Combustion of high-hydrogen-content fuels with low emissions poses some special challenges regarding the fuel injection and overall combustion system. To achieve low NOx emissions in the modern advanced combustion systems, the popular technique is burning the fuel in a lean pre-mixed manner, both for liquid and gaseous fuels. A high degree of pre-mixing of the fuel and air prior to combustion can lead to significant challenges when working with high hydrogen fuels, which may include autoignition, stability and flashback issues. Of these key operability issues, the most critical issue in this situation is flashback. The biomass gasification system output is nominally 50%-vol hydrogen/50%-vol carbon monoxide. The laminar flame speed and the reactivity of this fuel composition is much higher than that of natural gas indicating that this fuel will have a higher flashback propensity. As a result, the capability of burning highly reactive fuels (such as high-hydrogen-content syngas) in a lean, fully pre-mixed mode is a main focus of the gas turbine industry.
Other researchers have operated gas turbines on high hydrogen content fuels. Most of these previous works have focused on non-pre-mixed combustion systems. Some work with regard to the operation of pre-mixed systems on high hydrogen content fuels has also been carried out. General Electric and Siemens researchers have also investigated pre-mixed combustion systems for operation of gas turbines on high hydrogen content fuels. In general it is recognized that there are a few flashback mechanisms in a pre-mixed combustion system, namely, (1) core flashback; (2) boundary layer flashback; (3) flashback caused by combustion induced vortex breakdown dynamics and (4) flashback caused by combustion instabilities.